Accumulated Other Comprehensive Loss - Reclassifications from AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	$ (13,184)	$ (18,071)
Total net of tax	41,965	46,095
Interest expense	(59,897)	(36,587)
Total reclassifications, net of tax	(1,680)	(1,460)
Unrealized losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(548)
Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	16
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(1,036)
Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(157)	(101)
Tax effect	45	42
Total reclassifications, net of tax	(112)	(59)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(1,451)	(2,518)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Losses on securities transactions, net	(765)	(23)
Tax effect	217	10
Total net of tax	(548)	(13)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	(6)	(62)
Total net of tax	16	87
Interest and dividends on investment securities (taxable)	22	149
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	415	1,043
Total net of tax	(1,036)	(1,475)
Interest expense	$ (1,451)	$ (2,518)